Correction of a student project

For a programming course, we need to develop a little program in C which calculate Julia fractals. We receive a text file (where there are fractals "Name Height Width A B") and we need to calculate the fractal and return the fractal with the biggest average. We need to use multithread to improve the performance. I make my program but now I have problem... Sometimes de program work and sometimes no (segmentation fault and futex facility error). I need somebody to correct the program.